Shelf stability of reactive adhesive formulations: A case study for dicyandiamide-cured epoxy systems

Positron annihilation lifetime spectroscopy was used to study the curing behavior of epoxy resins of DGEBA with a hardener of dicyandiamide, from the initial viscous state of the formulation to the cured polymer. Isothermal measurements were done in the range from 50 to 80 °C. Gelation resulted in an increase of the intensity of ortho-positronium ( o-Ps) and a sharp decrease in the lifetime. Change of o-Ps lifetime was used as a measure for the degree of curing. Applying the Johnson–Mehl–Avrami–Kolmogorov approach, these changes could be characterized and growth exponent ‘ n’ and reaction constant ‘ k’ were determined. Hence, we are able to project the shelf life of this one-component epoxy at room temperature by extrapolation.